**Crystals are divided into seven systems. The
individual system distinctions are made according to the crystal axes and the
angles at which the axes intersect. There are also many sub-systems within
these main categories. The Isometric and Cubic systems are the same system with
alternative names. You may find an additional crystal system listed in some
sources, which is the Amorphous system. Amorphous “crystals” have no
crystalline structure because they cooled down too quickly to form any distinct
shape. In this category you will find material such as volcanic obsidian
varieties and meteoric tektites.Illustrations
and descriptions of the seven systems are listed below.

Isometric ~ Cubic System: All three axes have the same length and
intersect at right angles. The following crystal shapes can be found within
this system: Cube, Dodecahedron, Octahedron, Trapezohedron,
Diploid, Gyroid, Hexoctahedron,
Hextetrahedron, Tetartoid, Tetrahedron,
Tetrahexahedron, Trisoctahedron,
Tristetrahedron, Deltoid Dodecahedron, and Pyritohedron.

Hexagonal System: Three of the four axes are in one plane,
are of the same length, and intersect each other at angles of 60 degrees. The
fourth axis, which is a different length, is at right angles to the others. The
following crystal shapes can be found within this system: DihexagonalDipyramid, Dihexagonal
Pyramid, Hexagonal Dipyramid, DitrigonalDipyramid, Hexagonal Pyramid, Hexagonal Trapezohedron, and TrigonalDipyramid.

Trigonal
System: (Rhombohedral System) Axes and angles are similar to the
Hexagonal System, therefore the two systems are often combined as one system.
There is a difference in their symmetry. In the Trigonal
System the cross section of the prism base is three-sided. It is six-sided in
the Hexagonal System. The following crystal shapes can be found within this
system: Ditrigonal Pyramid, Hexagonal Scalenohedron, Trigonal Pyramid, Rhombohedron, and TrigonalTrapezohedron.

Tetragonal System: The three axes intersect at right angles,
two are of the same length and are in the same plane, while the main axis is
either longer or shorter. The following crystal shapes can be found within this
system: Tetragonal Dipyramid, Tetragonal Disphenoid, Tetragonal Pyramid, DitetragonalDipyramid, Ditetragonal
Pyramid, Tetragonal Prism, Ditetragonal Prism,
Tetragonal Scalenohedron, and Tetragonal Trapezohedron.

Orthorhombic System: Three axes of different lengths are at
right angles to each other. The following crystal shapes can be found within
this system: Pinacoid, Rhombic Prism, Rhombic Dipyramid, Rhombic Disphenoid,
Rhombic Pyramid, and Rhombic Tetrahedron.

Monoclinic System: The three axes are each ofdifferent lengths, two are at right
angles to each other, and the third one is inclined. The following crystal
shapes can be found within this system: Domatic,
Prismatic, Sphenoid, and Pinacoid.

Triclinic System: All three axes are of different lengths,
none of which are perpendicular and inclined to the others. Typical crystal
forms are paired faces. The only regular forms recognizable in Triclinic
crystals are the two parallel faces of the Pedion and
the Pinacoid. The Pinacoid
face has no symmetrical relationship to any other.

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